Optical methods for data storage and retrieval are in widespread use in computer technology, as well as audio and video recording. Among the various descriptive terms used to describe the present state of the art are CD (Compact Disk), Laser Disk, and CD-ROM (Compact Disk Read Only Memory).
Optical disks store data in the form of small oblong pits that cause fluctuations in the brightness of a laser beam illuminating a surface of the disk. Arrays of microscopic, optically distinct regions form tracks or sectors located on the background material supporting these tracks. These tracks are arranged to represent a sequence of digital data. The data is read or retrieved from the disk by illuminating the region of interest with the light of a laser focused on individual regions in a specific sequence. The difference between reflected or transmitted light is discerned by an optical detector. These light fluctuations are then converted into a stream of ones and zeros, and thus into information that the user receives as numerical data, which may be further interpreted as text, image, sound, or a combination of the three.
Various approaches have been taken to increase the density of data storage on the disk. Some of these approaches are described in U.S. Pat. No. 5,247,510 entitled "Increasing Storage Density of Optical Data Media by Detecting a Selected Portion of a light Spot Image Corresponding to a Single Domain," and U.S. Pat. No. 5,161,134 entitled "Method For Increasing Linear Density In Magneto Optical Storage Media." As revealed in these patents, an increase in density of optical data storage has depended mainly on improvements in the resolution of the hardware for locating and distinguishing among closely spaced variations in a two-dimensional distribution of marks. These techniques permit closer spacing of the data-bearing indicia thus increasing the density of the storage medium.
Dealing with a two-dimensional storage medium, such as a conventional compact disk, the above approaches are ultimately limited by the two-dimensional surface area of the medium, despite the improvements in the resolution of the optical hardware.